1. Field of the Invention
This invention relates to synthetically derived high density liquid hydrocarbon fuels.
2. Description of the Prior Art
High density liquid hydrocarbon fuels are characterized in having a net volumetric heat of combustion in excess of about 140,000 BTU per gallon. A high density or energy fuel is essentially required for fueling turbojet and ramjet propelled limited volume missile systems. Beyond the need for a high energy content in order to maximize range performance of the missile, there are other requirements in the forefront depending, in the main, on the manner in which the missile is to be deployed. For instance, in the airborne deployment of a missile where the latter is carried exteriorly of the aircraft, the fuel must exhibit the combination of a very low freeze point and high volatility.
A high density fuel of the foregoing type does not occur in nature but rather must be chemically synthesized. Essentially all of the current generation of such fuels commonly feature a norbornane moiety having an additional cyclic hydrocarbon appendage. Such appendages include the norbornane structure itself in the case of the most exotic of these fuels designated RJ-5; viz., dihydro di (norbornadiene), otherwise referred to as the hydrogenated dimers of norbornadiene. In some instances only a specific stereo isomer of the synthesized compound represents a suitable fuel from the standpoint of having the requisite physical properties. A notable example of this is JP-10 which chemically is the exostereo isomer of tetrahydrodicyclopentadiene.
In missile launching situations calling a low temperature operational capability as noted above, the foremost fuel of choice is said JP-10. This is so because JP-10 is derived from abundantly available raw materials coupled with the comparative ease of preparing a given chemical species as opposed to preparing complex mixtures thereof with attendant reproducibility problems. There is, however, a drawback to the use of JP-10 in airborne launching operations insofar as it possesses relatively low volatility thereby resulting in an unacceptably high flash point of about 130.degree. F. For the indicated low temperature operations, a flash point of less than 100.degree. F. and preferably substantially less that this value is sought.
The foregoing volatility requirement has been met by a fuel designated JP-9, same being a blend of 65-70 weight percent JP-10, 20-25 weight percent RJ-5 and 10-12 weight percent methylcyclohexane. Methylcyclohexane serves to impart the necessary volatility characteristics to JP-10, so that an acceptable flash point can be realized. However, this low density component is required in an amount which undesirably lowers the volumetric heat of combustion of JP-10. Therefore, it is necessary to include the indicated amount of RJ-5 in order to achieve an overall volumetric heat of combustion in the order of that exhibited by neat JP-10.
As mentioned previously, RJ-5 is the most exotic of the current high density fuels in that it possesses a heat of combustion in excess of 160,000 BTU per gallon. It is, however, by far the most expensive of the high energy fuels due in part to the difficulty in synthesizing the fuel itself and in a larger part due to the short supply of the precursor, norbornadiene, from which it is prepared. It is accordingly the object of the present invention to provide a high density fuel having the heat content and physical properties established for JP-9 but which does not require the use of RJ-5 to extent specified for JP-9.